In contemporary aircraft, ram air turbines (RAT) are used to provide emergency power, given a failure of the engines, generators or hydraulic systems, by generating a free flow toward the rotor. The ram air turbines are here within an aerodynamic cladding when non-operative, and are mechanically folded out in emergency situations.
Depending on the system configuration of the aircraft, the ram air turbine rotor shaft driven by the stream of air powers a hydraulic pump, or an electric generator. The energy of the ram air turbine is here used above all for primary flight control.
The ram air turbine system is mechanically complex in light of the deployment mechanism (out folding mechanism) and rotating components. The system performance decreases with diminishing flight velocity and decreasing outside pressure, while the need for emergency power is particularly high precisely before or while landing. The ram air turbine and its operability cannot be permanently monitored. The ram air turbine can only ensure full power at a flow that is as uninfluenced as possible by the aircraft boundary layer. For this reason, integrating the ram air turbine into the aircraft is a complicated process.